The invention relates to an ultrasonic monitoring device, and in particular to a real-time ultrasonic device for monitoring machine part surface topography and tool condition in situ.
The invention applies to a large range of surface topographies from the microscopic, where the surface feature dimensions are very small and typically expressed in microinches, to the macroscopic where the surface features are much larger. A descriptor often associated with a microscopic topography is "average surface roughness" (or simply "surface roughness") because the measuring probe typically averages over a region much larger than the region of an individual feature such as a surface peak or valley. Measuring the detailed shape of individual features, whether it be microscopic or macroscopic in scale, may be referred to as surface profiling.
Traditionally, the machine tool operator may evaluate the surface roughness of the machined part by tactile sensing and visual observation of the stationary part and perhaps assign some quantitative measure by comparing his sense touch to that of a set of roughness artifact standards thereby indicating the condition of the tool. A stylus gauge may be used to provide a more precise roughness measure by traversing in direct contact a section of the stationary part which yields an average value of the surface topography over that section.
More recently, ultrasonic techniques have been used to determine surface roughness of parts. The basic concept of the ultrasonic technique is that the back scattered energy from an impinging ultrasonic wave is a sensitive function of the surface roughness. Examples of such prior art monitoring techniques may be found in U.S. Pat. Nos. 4,364,264 issued to Fiorentin and 3,688,569 issued to Murdoch, both of which are incorporated herein by reference.
Fiorentin measures surface roughness of a part based upon a phase measurement. A measurement probe, in contact with a surface to be measured, transmits an ultrasonic pulse to the surface and receives a reflection of the transmitted pulse from the surface. The phase difference of the reflection is indicative of the surface roughness of the part. However, the device is useful only when the probe comes in contact with the surface of the part.
Murdoch measures surface roughness by immersing the part in a liquid couplant, transmiting ultrasonic energy to the surface of the part in the couplant and measuring the amount of ultrasonic energy reflected from the surface in order to provide an indication of surface roughness. However, this procedure is limited to stationary parts and has no utility in the area of monitoring surface finish or tool conditions in-situ.
Applications of ultrasound measurement techniques further extend to the inspection of part dimensions, such as thickness. An example of such a prior art inspection technique may be found in U.S. Pat. No. 4,403,510 issued to de Walle et al incorporated herein by reference. Further, the prior art provides nozzle structure teachings such as shown in Djordjevic et al, U.S. Pat. No. 4,507,969, for the sending of fluid and ultrasonic waves through the fluid in laminar flow to the part in order to create an echo within the part. However, the echo amplitude from the interior of the part indicates only interior inhomogeneities and not surface roughness. Furthermore, the prior art is limited in that it is effective only when the laminar flow carrying the ultrasonic wave flows in a nearly straight line from the ultrasonic sending device to the part. Once the fluid is no longer disposed in a straight-line flow, the ultrasonic wave becomes distorted.
Additionally, since the nozzle must be close to the surface of the part in order to achieve a straight-line flow, the prior art is not always effective in an on-line approach to monitoring surface topography or dimensional characteristics at various locations on a machined part. Given the speed of rotation (for example, surface speeds on the order of 1000 ft/min) of a part as it is being machined, it is difficult and usually impossible to place the prior art measurement probes or nozzles close to the surface of the part. The advantage of an on-line approach is not only the real-time evaluation of surface condition, but also the capability to provide sensor feedback for machine control, and a means to evaluate tool condition in terms of its performance on the part. This requires information about surface roughness in areas on a machined part not currently capable of measurement using prior art devices.
Thus, it is an object of the present invention to provide an ultrasonic system capable of real-time recording of surface topography of a machined part in an on-line situation.
Another object of the present invention is to provide a system capable of monitoring part surface topography in order to determine tool condition in situ.
A further object of the present invention is to provide a device capable of employing the ultrasonic technique of transmitting ultrasonic waves through a fluid in laminar flow when the laminar flow cannot travel in a straight line.
Other objects and advantages of the present invention will be readily apparent from the following description and drawings which illustrate a preferred embodiment of the present invention.